1. Field of the Invention
This invention relates to a picking device for a water-jet loom and, more particularly, to a picking device capable of picking a plurality of different kinds of weft yarns in sequence or periodically.
2. Description of the Prior Arts
A water-jet loom needs a plurality of fluid passages and a fluid passage selecting device, such as a selector valve, for selectively supplying a pressurized fluid to the plurality of fluid passages to pick a plurality of different kinds of weft yarns in sequence or periodically.
As shown in FIG. 21, by way of example, in a conventional water-jet loom disclosed in Japanese Utility Model Unexamined Publication (Kokai) No. 63177975, two picking devices 101a and 101b are disposed close to each other, the picking devices 101a and 101b are connected to an electromagnetic or mechanical selector valve 103 respectively by water supply lines 102a and 102b, and the selector valve 103 is connected to a pump 100.
Generation of a high-velocity water jet is essential to enable a-water-jet loom to operate at a high weaving speed. A water-jet loom needs only one picking device and one water supply line if the loom uses a single kind of weft yarn, and so the water supply system of the water-jet loom need not be provided with any selector valve and requires only a comparatively simple control operation. Generally, such a water-jet loom provided with a single picking device is provided with a pump having a pressure capacity in the range of 70 to 80 kg/cm.sup.2 and is capable of operating at 1200 rpm, i.e., 1200 picking cycles per minute, at maximum.
A water-jet loom that uses a plurality of kinds of weft yarns needs a water supply system provided with a plurality of water supply lines respectively for the plurality of different kinds of weft yarns and, as shown in FIG. 21, a selector valve. Pressure loss in the pressurized water due to the frictional resistance of the pipes forming the water supply lines and the resistance of the restrictive portions of the selector valve against the flow of water is not ignorable. If the pressure loss is excessive, sufficient water cannot be supplied to each picking device. The maximum pressure capacity of a pump suitable for use on the conventional water-jet loom provided with a plurality of picking devices is on the order of 140 kg/cm.sup.2, the maximum weaving speed of the conventional water-jet loom is on the order of 700 rpm, and the water-jet loom provided with a plurality of picking devices consumes 1 to 1.3 cm.sup.3 /pick (1 ton/day) more water than a water-jet loom provided with a single picking device.
The water-jet loom capable of picking a plurality of kinds of weft yarns in sequence or periodically needs a pump with a considerably large pressure capacity, inevitably entailing an increase in power consumption and pump noise, and a reduction in the functional lives of the pump and the selector valve due to enhanced abrasion. Other problems are that water hammer occurs when the selector valve changes the water supply line, damaging the weft yarn, and that the operating costs, including power and water cost, are very high.
In the conventional water-jet loom, the picking devices and the peripheral parts have complicated constructions, and so it is difficult to provide the water-jet loom with three or more picking devices due to the geometrical relation between the picking devices and the size of the shed.
Still further, since the conventional water-jet loom provided with a plurality of picking devices has a plurality of water supply lines and a selector valve supplying water selectively and sequentially to the water supply lines, water supplied to one water supply line leaks into another water supply line. This means that insufficient water is supplied to the former water supply line, which often entails short pick or bent pick.